Recent efforts to understand global patterns of ant diversity have largely neglected the canopy which harbours a diverse ant fauna, particularly in tropical lowland forests. We comprehensively sampled ant diversity and abundance by canopy-fogging in South-East Asian lowland rain forests (99 trees fogged, 151,396 ant individuals, 328 morphotypes) and in Central European temperate forests (375 trees fogged, 9,232 ant individuals, 12 species). We found large differences in taxonomic composition, diversity, and overall abundance of the canopy ant communities in both biomes. Our data suggest that in the tropics approximately 50% of all ant species are at least partially associated with the canopy. Taxonomic work on selected groups of ants suggests that a substantial proportion of these species are new to science. Due to high habitat specificity canopy ants previously were out of reach for ant collectors and have thus largely remained unrecorded. Canopy ants therefore have been neglected in ecosystem analyses or global diversity modelling. In contrast, in temperate forests only 12% of the species are known to be arboreal and ants rarely achieve dominance in the canopy. The large difference in abundance and species numbers in the canopy of temperate and tropical forests suggests major differences in the ecological and functional impact of canopy ants.